When I built my house 4 years ago I did not put cans above my bar. My wife is now thinking that we should do that. I want to tie into an exsisting light above the sink. I am wondering if I can just run wire from that light, to can 1, then to can 2. Connecting whites to whites, black to black, and grounds to grounds?

Sounds good to me! Just note that the existing light above the sink will be on with the lights above the bar.